This application claims priority of the German patent application 101 15 837.8 which is incorporated by reference herein.
The invention concerns a stand, in particular for a surgical microscope. The purpose of such stands is to hold a relatively heavy microscope so that it is movable by an operator with a minimum of resistance. An effort is therefore made to configure all joints, bearings, and the like in as low-resistance a fashion as possible, so that as little resistance as possible is presented to any arbitrary movement by the user.
In surgery but also in other areas of technology, for example microelectronics, forensics, etc., more and more use is being made of surgical microscopes that, because of their heavy weight, must be supported by stands. Several well-known manufacturers have marketed stands that are well suited, in terms of mechanics and statics, for supporting the load of a surgical microscope. The present applicant, for example, markets stands with the designation OHS or MS1. One example of such a stand is found in EP-A-628290. Zeiss/Deutschland has disclosed a stand, for example, in EP-476552.
Many modern stands have parallelogram supports to allow the load of the surgical microscopes to be carried over the greatest possible distances with no bending or twisting, in order to maximize the freedom of movement and radius of action of the microscopes. In principle, however, the greater the radius of action, the greater the instability of a stand, except if appropriate design actions are taken against instability. However, the more rigid (less unstable) the structures, the more susceptible they are to vibratory behavior, which is similarly counteracted with design features such as selection of varying tube cross sections, material selection, use of damping elements, etc.
The transported weight of the stands also represents a problem whose solution lies fundamentally in weight reduction by means of high-strength materials.
For example, the present applicant has created a stand that uses at least one support made of a fiber-reinforced plastic. This stand is described in the aforementioned WO-A-97/20166.
It has been recognized, however, that weight reduction alone is not sufficient in some circumstances if the quality of the damping properties of the essential components is not sufficiently taken into account. Mere weight reduction results in some circumstances in intensified, higher-frequency vibratory behavior in the structure. This vibratory behavior is amplified in structures having braked arms. Brakes of this kind are to be operated electromagnetically, pneumatically, or even by hand, and create a rigid connection between the components, so that vibrations are transmitted from one component to another and result in a long vibration period that is annoying to the user.
The route of weight reduction by means of fiber composite materials and plastics has been taken in another sector of stand design, namely X-ray technology, as set forth in DE-C1-42 14 858. In this, a C-curve was created from plastic foam as the supporting part that determines the shape, which is surrounded by a fiber-reinforced plastic that assumes the support functions. If this known assemblage is to be particularly light in weight, then according to this previously published teaching a profile of closed shape must be produced from (only) fiber-reinforced plastic. Composite material structures of this kind have inherently low vibratory characteristics.
In stands for the applications mentioned, however, there exist joints, rotary bearings and the like in which vibratory behavior can occur regardless of the quality of the other components. One such point, for example, is the vertical rotary bearing on a vertical upright column for the horizontal carrier arm or arms of the stand. Proceeding from such bearing points, which as a rule can be immobilized using brakes, movements or forces on the microscope also create torsional forces which in turn can preferentially excite torsional vibrations in the components that are loaded in torsion.
For particular vibration damping, the present applicant has already offered solutions that are recited, for example, in WO-A-98/53244. In this, inter alia, elastically damping layers which act to damp the vibration chain from the microscope to the floor are installed under the mounting feet of the tripod foot. With these known assemblages, even the slightest change in the position of the microscope causes a vibratory excitation which nevertheless, once it has passed through the stand, is damped at the mounting feet and therefore reflected only in attenuated fashion.
Damping plates that are inserted between stand components have also been proposed, for example damping shoes at the transition from a support tube to a support tube mount, or damping plates between two flanges of two adjacent support tubes or between a tube and a pedestal.
The advantage of such damping elements in the region of the upper body of the stand is that they help damp the vibrations on their initial path from the microscope to the floor, so that need not even pass through the entire stand. The effectiveness of these known damping shims lies in the damping effect that occurs upon compression of these damping elements, i.e. for example when the tube vibrates in its shoe in the axial direction of the tube or in a direction perpendicular thereto (tilting vibration), or if the mounting feet are loaded in terms of pressure load fluctuations due to vibration of the upright column in a vertical plane.
Attempts to damp torsional vibrations have hitherto been made by way of a particular configuration of the support tubes. For example, aluminum/composite plastic tubes or carbon fiber-reinforced plastic tubes have been created, in which torsion in the tube was counteracted by specific selection of the fiber plies. The OHS of the present applicant that is configured in this fashion has low torsional behavior, however, not only as a result of good selection of the supports, but also because of the balanced configuration about the rotation axis in the upright column. In this known assemblage, the center of gravity of the moving carrier arms and balancing arms lies directly above or in the immediate vicinity of the upright column. Other stands in which the center of gravity of the moving carrier arms is well to the side of the upright column amplify the torsional vibration behavior, especially if the stand is braked via the rotation axis. Mere application or release of the brake, or the slightest movements of the microscope, can generate torsional vibrations.
Torsional vibrations (often horizontal vibrations) are substantially more deleterious in microscopy than vertical vibrations, in particular because in the case of a vertical vibration, the depth of focus that is always present means that a slight vibration is not noticed. Horizontal vibrations, however, result in a severe negative impact when observing through the microscope.
It is the object of the present invention to find solutions which improve the vibratory behavior of the stand, i.e. suppress vibration or optimally damp any vibrations, without thereby sacrificing precise positioning accuracy. The intention in particular is to counteract low-frequency torsional vibrations, e.g. in the range of, for example, 0 to 10 Hz. The new features are intended to effectively counteract torsional vibrations and optionally to be usable in combination with known vibration damping features.
Those skilled in the art know that such objects are difficult to achieve, and that the application of mathematical and physical resources and theories often does not bring the expected results. On the other hand, however, even slight improvements are worth striving for, since they improve convenience for the user and consequently increase operating safety. According to the present invention, this object is achieved by way of a microscope stand, in particular for surgical microscopes, having vertical and horizontal supports and a vibration damper, wherein the vibration damper is configured as a torsional damping element.
The invention thus offers, for the components necessarily present on a stand for a surgical microscope, particularly suitable and tuned damping elements with low weight and improved vibratory behavior. The specifications of stand support parts in terms of their vibratory behavior can be slightly reduced, which in this context can result in cost decreases.
Further specific embodiments and variants thereof are described and protected in the claims. The properties of the preferred material lie within approximately the following parameters:
measured in each case on the basis of DIN 53513. The preferred material selected is, by way of example, Sylomer(copyright) M12, Sylomer(copyright) M25 P14 or Sylomer(copyright) P12, Sylomer(copyright) P25 P15, or in particular Sylodamp(copyright) HD-010-11, HD300/1, HD-030-11, HD-050-21, HD-100-11, HD-150-12, HD-300-10 or 12, but preferably HD-300-1 for the dynamic load range from 0 to 0.3 N/mm2.
The dissipation factor at 8 Hz per ISO 10846-2 should preferably be more than 0.1, in particular more than 0.2, at a strain at fracture per DIN 53455-6.4 of more than 100%, preferably more than 200%, and in particular approximately 300%.
Such materials are available under the designation SYLODAMP(copyright) from Getzner Werkstoffe GmbH, Bxc3xcrs (Austria).
Damping materials can also be combined if necessary. Variants with specific shaping of the damping materials also lie within the context of the invention. For example, recesses such as blind holes or the like can be provided in order further to influence the damping characteristics.
Sandwich constructions of different damping materials can be used, for example, for improved torsional stiffness.